Sol-Gel Nanometrology: Gated Sampling Can Reveal Initial Sol Formation Kinetics

This report describes a gated sampling approach for studying the initial formation of sol-gel glasses prepared from sodium silicate solution (water glass) and sulphuric acid. Previously described were how changes in particle size and subsequently how sol-gel formation dynamics can be tracked using time-resolved fluorescence anisotropy, by labeling growing silica nanoparticles with suitable fluorescence probes. One limiting factor of this approach was the 2 minute measurement time, which limits this technique for studying the initial sol formation dynamics and limits the measurement precision. Using a continuous flow system and delaying sol flow through different tubing lengths overcomes this problem and allows monitoring of the very early stages of sol formation, second by second after sol preparation, irrespective of the anisotropy measurement time. This technique was applied to studying the initial formation dynamics, within the first 30 seconds, of a 12.01% SiO₂ (w/w), pH 0.66 sol-gel, finding that silica particles of 1.5 nm mean radius are formed within 10 seconds of mixing the sol-gel.     

Probing the Sol-Gel Transition in SiO2 Hydrogels—A New Application of Near-Infrared Fluorescence

Picosecond time-resolved fluorescence spectroscopy has enabled us to use a near-infrared fluorescent dye to probe the sol-gel transition in SiO₂ hydrogels, polymerized from sulfuric acid and sodium silicate solution, for the first time. We compare the microviscosity surrounding the probe during the sol-to-gel transition as predicted by two alternative models which both describe the decay of fluorescence anisotropy well. The results for one rotational time and a residual anisotropy imply that macrogelation of the sol leads to relatively small changes in the mobility of the fluorophore caused by small changes in microviscosity, but after much longer times, e.g., 1500 min, the mobility of the fluorophore decreases, reflecting a rapid increase in microviscosity of over several orders in magnitude. In sharp contrast, analysis of the anisotropy in terms of two rotational times predicts little change in microviscosity over the whole polymerization process.     

Epoxy/Silica Nanohybrids or Nanocomposites: Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Investigation of the Processing–Structure–Property Relationships

The structural and morphological features influencing the glass transition temperature of epoxy/silica nanohybrid and nanocomposite materials containing 25–30 phr of nanoscale silica phases are discussed in this letter to answer the questions related to the processing–structure–property relationships. X-ray photoelectron spectroscopy and atomic force microscopy are used to study the surface chemical structure and morphology of epoxy/silica nanohybrids and nanocomposites. Nanohybrids are synthesized via in situ sol-gel process, while the respective nanocomposites are prepared by mechanical blending of preformed silica nanoparticles into epoxy resin. Differential scanning calorimetry is used to determine glass transition temperature of different materials. The surface analytical characterizations reveal that in situ sol-gel process is more suitable for producing organic–inorganic hybrid materials with superior glass transition temperature owing to the achievement of stronger interfacial compatibility and greater crosslink density. A number of other factors affecting glass transition temperature are explored and discussed with reference to surface chemistry, microstructure, and morphology of epoxy/silica nanohybrids and nanocomposites, respectively.     

Steady-State and Time-Resolved Fluorescence Polarization Behavior of Acenaphthene

Steady-state and time-resolved fluorescence polarization studies have been carried out on acenaphthene (ACE) in low-temperature glass solutions and at room temperature. In the low-temperature glass the fluorescence polarization values vary considerably with both emission and excitation wavelength. There is a time dependence (on the nanosecond time scale) of the fluorescence anisotropy, r(t), at 77 K, which has a strong dependence upon the excitation and emission wavelengths. Under these conditions, the time-dependent decay of the anisotropy is not attributable to chromophoric motion. The observations are consistent with emission from two closely lying and interconverting excited states. Rate constants for the photophysical processes involved have been determined by fitting the data using a model proposed by Fleming et. al. The results are discussed with particular reference to the care required in using dynamic fluorescence polarization measurements to determine energy transfer rates in systems containing this chromophore.     

基于芘功能化核壳型磁性二氧化硅纳米微球的荧光传感器及其对水溶液中汞离子的检测和去除

通过溶剂热、溶胶-凝胶和共嫁接技术开发制备了一种基于芘功能化的核壳型磁性二氧化硅纳米微球的可回收汞离子光学传感器。相对于其他竞争金属离子,获得的多功能纳米微球对Hg²⁺具有良好的荧光传感性能和选择性。多功能微球的荧光强度与Hg²⁺浓度之间显示出良好的Stern-Volmer线性关系（R²=0.998 3）,其检测限为2.3×10^-8 mol·L^-1。该材料对汞离子的荧光响应具有可逆性,利用EDTA溶液处理可实现多次重复使用。此外,芘功能化的磁性二氧化硅纳米微球可以有效地除去水溶液中的Hg²⁺,并且通过施加外部磁场可实现简单快速的分离。上述结果表明,这种功能化核壳型磁性二氧化硅微球在同时检测和去除环境污染物方面具有良好的发展前景与应用潜力。     

Spectroscopic study of sulforhodamine 640-doped sol-gel silica

The sol-gel process is a technique which provides a low-temperature route for the preparation of organic dye-doped porous silica glass. Extended UV transmission was observed for HCl-catalysed sol-gel silica. Properties of a solute may differ greatly between a free solution and that solution confined in pores of a sol-gel glass. Absorption and fluorescence properties of sulforhodamine 640-doped silica samples prepared by sol-gel process were investigated. In the TEOS-derived gel, the emission of the dye does not shift during aging but exhibits a large change during drying. The emission maximum of sulforhodamine 640 blue shifts was discussed as a function of increasing rigidity of the surrounding matrix.     

Structural and Optical Properties of Gold/Silica “Mushroom” Particles Prepared by Interfacial Templating

Complex shaped nanoparticles featuring structural or surface chemical patchiness are of special interest in both fundamental and applied research areas. This study reports the preparation and optical properties of gold/silica “mushroom” nanoparticles, where a gold particle is only partially covered by the silica cap. The synthetic approach allows precise control over the particle structure. The interfacial preparation method relies on partially embedding the gold particles in a polystyrene layer that masks the immersed part of the gold particle during silica shell growth from an aqueous solution. By adjusting sacrificial polystyrene film thickness and silica growth time, precise control over the coverage and cap thickness can be achieved. Correlative electron microscopy and single particle scattering spectroscopy measurements underline the high precision and reproducibility of the method. The good agreement between the measured and simulated single particle spectra supported by near‐field calculations indicates that the observed changes in the dipolar plasmon resonance are influenced by the extent of coverage of the gold core by the silica cap. The straightforward methods readily available for gold and silica surface modification using range of different (bio)molecules make these well‐defined nanoscale objects excellent candidates to study fundamental processes of programmed self‐assembly or application as theranostic agents.     

Flow with photon multiplicity detector: Past and future

Measurements of azimuthal distribution of inclusive photons using the fine granularity pre-shower photon multiplicity detector (PMD) at CERN SPS are used to obtain anisotropy in the azimuthal distributions. These results are used to estimate the anisotropy in the neutral pion distributions. The results are compared with results of charged particle data, both for first order and second order anisotropy. Assuming the same anisotropy for charged and neutral pions, the anisotropy in photons is estimated and compared with the measured anisotropy. The effect of neutral pion decay on the correlation between the first order and the second order event plane is also discussed. Data from PMD can also be used to estimate the reaction plane for studying any anisotropy in particle emission characteristics in the ALICE experiment at the large hadron collider (LHC). In particular, we show that using the event plane from the PMD, it will be possible to measure the anisotropy inJ/Ψ absorption (if any) in the ALICE experiment.     

Domain Formation in DODAB–Cholesterol Mixed Systems Monitored via Nile Red Anisotropy

The effect of the cholesterol (ch) on liposomes composed of the cationic lipid dioctadecyldimethylammonium bromide (DODAB) was assessed by studying both the steady-state and time-resolved fluorescence anisotropy of the dye Nile Red. The information obtained combined with analysis of the steady-state emission and fluorescence lifetime of Nile Red (NR) for different cholesterol concentrations (5–50%) elucidated the presence of “condensed complexes” and cholesterol-rich domains in these mixed systems. The steady-state fluorescence spectra were decomposed into the sum of two lognormal emissions, emanating from two different states, and the effect of temperature on the anisotropy decay of Nile Red for different cholesterol concentrations was observed. At room temperature, the time-resolved anisotropy decays are indicative of NR being relatively immobile (manifest by a high r _∞ value). At higher temperature, rotational times ca. 1 ns were obtained throughout and a trend in increasing hindrance was seen with increase of Ch content.     

SiO2干凝胶中CdS量子点的光致发光性质

以正硅酸乙酯(TEOS)为SiO2的前驱物,硝酸镉为镉源,硫脲为硫源,用溶胶-凝胶法制备了CdS量子点掺杂的SiO2干凝胶,利用XRD、紫外-可见吸收光谱、光致发光谱对其性质进行研究.样品的测试结果表明在SiO2干凝胶的网状结构中形成了CdS量子点,平均粒径为5.1 nm.SiO2凝胶中CdS吸收峰位置明显蓝移.在一定...     

Electronic deactivation and energy transfer in doped oligophenylenevinylene nanoparticles

Suspensions of oligophenylenevinylene (nPV) nanoparticles withn = 2 vinylene units are doped with nPVs of longer chainlengths,n = 3–5. Absorption and fluorescence spectroscopy and steady-state and time-resolved fluorescence anisotropy measurements are used to determine the photo-physical properties of the suspensions. Undoped nanoparticles form highly oriented H-aggregates with low fluorescence quantum yields (Φ_F ≈ 0.1). Introduction of bulky substituents into the particle constituting molecules perturbs the intermolecular orientation. Upon doping, efficient energy transfer to the dopants is found, changing the color and leading to enhancement of the fluorescence quantum yields up to Φ_F = 0.6. The intermolecular orientation is not changed upon doping.     

Fluorescence anisotropy decay study of self-association of bacterial luciferase intermediates

The fluorescence dynamics parameters of the fluorescent transient flavin-luciferase species from the typesVibrio fischeri andPhotobacterium leiognathi are presented. The fluorescence anisotropy decay is a single exponential function for both types. The correlation time is 70 ns for theP. leiognathi fluorescent transient intermediate (2°C, aqueous buffer, pH 7.0), consistent with the rotational correlation time of the luciferase macromolecule (77 kD) to which the flavin fluorophore is rigidly attached. In contrast, for theV. fischeri species the observed correlation time for the anisotropy decay function is 133 ns. This suggests that protein self-association occurs in theV. fischeri case and this is confirmed by filtration, where the fluorescent transient fromV. fischeri does not pass through a 100,000 molecular weight cutoff membrane, whereas theP. leiognathi species does. The filtration method also demonstrates self-association in the luciferase peroxyflavin and photoflavin fromV. fischeri. A monomer-dimer equilibrium also explains the previously reported high correlation times for theV. harveyi luciferase-flavin species. It is proposed that the self-association competes with the lumazine protein interaction in the bioluminescence reaction.     

Surface effect on the size evolution of surface plasmon resonances of Ag and Au nanoparticles dispersed within mesoporous silica

The optical absorption has been investigated for silver and gold nanoparticles dispersed within the pores of monolithic mesoporous silica after annealing at different temperatures. It has been shown that with reduction of the particle size, the surface plasmon resonance position blue-shifts first and then red-shifts for silver/silica samples, but only red-shifts for gold/silica samples. This size evolution of the resonance is completely different from that previously reported for fully embedded particles. Based on the interaction of the particle surface with ambient air and the porosity at the particle/matrix interface, we present a multi-layer core/shell model and assume that the chemical adsorption of gas molecules from the air on the free surface of nanoparticles within the pores is mainly responsible for the observed size evolution of the resonance.     

Energy transfer between the flavin chromophores of electron-transferring flavoprotein fromMegasphaera elsdenii as inferred from time-resolved red-edge and blue-edge fluorescence spectroscopy

Both a mode-locked argon-ion laser and synchrotron radiation were used as excitation sources to obtain time-resolved polarized fluorescence of the two FAD cofactors in electron transferring flavoprotein fromMegasphaera elsdenii. Red-edge excited and blue-edge detected fluorescence anisotropy decay curves did not contain a fast relaxation process which was observed upon mainband excitation and detection. This relaxation was assigned to homo-energy transfer between the two FAD cofactors. Failure of energy transfer as observed with edge spectroscopy on this protein excludes restricted reorientational motion of the flavins as a possible mechanism of depolarization. From the global analysis of the fluorescence anisotropy decay surface obtained at multiple excitation and detection wavelengths, the distance between and the relative orientation of the flavins could be estimated. The methodology described has general applicability in other multichromophoric biopolymers and has the potential to acquire accurate geometrical parameters in these systems.     

Remarkable enhancement of magnetization in the superconducting state of In/Ni nanoparticle composites by inhomogeneous spin anti-screening

The enzymatic hydrolysis of quinizarin diester in silica nanoparticle (NP) of 200 nm diameter is investigated by confocal fluorescence microscopy. The quinizarin diester substrate and the intermediate quinizarin monoester are non-fluorescent species and only the end product—quinizarin formed by enzymatic hydrolysis produces intense fluorescence of the silica NP. The enzyme activity of lipase adsorbed into silica NP was similar to that observed for lipase chemically bound to silica surface. In both situations, partial aggregation of the silica NP dispersed in thin film of polyvinylpyrrolidone was observed from fluorescence and scanning electron microscopy images. The fluorescence decay of the end product—quinizarin in silica NP was biexponential with decay times of 0.49 and 2.17 ns. These two decay times found are ascribed to quinizarin adsorbed in silica NP and dispersed in the surrounding medium, respectively.     

聚电解质包覆的铕(Ⅲ)配合物@SiO2荧光纳米粒的合成与性质

以二苯甲酰甲烷(DBM)、邻菲罗琳(phen)和丙烯酸(AA)为配体,制备了铕的配合物Eu(Ⅲ)(DBM)2-(phen)(AA).利用St(o)ber法合成了SiO2纳米粒.通过超声辅助,将脂溶性的强荧光铕配合物吸附到SiO2纳米粒上,再包覆阳离子聚电解质聚二烯丙基二甲基氯化铵(PDAC)和阴离子聚电解质聚丙烯酸(P...     

Dynamics ofLens culinaris agglutinin studied by red-edge excitation spectra and anisotropy measurements of 2-p-toluidinylnaphthalene-6-sulfonate (TNS) and of tryptophan residues

The fluorescence of 2-p-toluidinylnaphthalene-6-sulfonate bound toLens culinaris agglutinin and of the Trp residues of the protein was investigated. Red-edge excitation spectra and steady-state anisotropy as a function of temperature indicate that the TNS is bound rigidly. Red-edge excitation spectra, steady-state anisotropy as a function of sucrose and anisotropy decay experiments performed on Trp residues fluorescence prove that the internal fluorophore presents residual motion independent of the global rotation of the protein. Fluorescence anisotropy decay allows to calculate the rotational correlation time (351 ps) of this local motion. Quenching resolved emission anisotropy with iodide gives values equal to 0.257 and 0.112 for the anisotropies of the buried and the surface Trp residues, respectively. This result indicates that the Trp residues present at the surface of the protein have important local motions compared to those embedded in the protein matrix. The results obtained from TNS and Trp residues indicate that the agglutinin has different dynamic domains.     

Laser and fluorescence properties of dye-doped sol-gel silica from 400 nm to 800 nm

Lasing and fluorescence properties of ten dyes covering the spectral range from 400 nm to 800 nm were studied in a silica matrix prepared by the sol-gel technique. The dye-doped sol-gel silica samples fluoresced strongly under laser excitation. Many of the samples were also induced to superradiate. In comparison to dyes in alcohol solvents, significant red-shifting was observed in the sol-gel silica fluorescence spectra. Plausible causes of the red-shift are discussed.     

The Influence of Solvent Viscosity on the Fluorescence Decay and Time-Resolved Anisotropy of Green Fluorescent Protein

This report describes fluorescence decay and time-resolved anisotropy studies of green fluorescent protein (GFP) in various environments. The addition of glucose and fructose, NaCl, or polyethylene glycol changes the viscosity of the medium surrounding the GFP. Both the time-resolved anisotropy and the fluorescence decay of GFP are measured and it is shown that only the time-resolved anisotropy of GFP is affected by the viscosity, but not its fluorescence decay.